Does this comply with 314?

[Deleted account]

It is a new Reg in the 18th Ed draft, 10% of the rated residual operating current of the device.

Thanks for that westward. I've checked your post #30. That's interesting to know.
I've now got my books out( 17th edition that is) and I still cannot find where I've think I've seen 25% of rated residual current as a design guidance. Therefore a 30mA rcd should be designed with7.5mA as its max.
I know I've seen it somewhere.

I'm wandering where the 30% 9mA came from.

 

[westward10]

I believe some guide books may quote this figure as it is some "rule of thumb" rcbos are prone to unwanted tripping once a 25% threshold of their rating tripping current is reached.

 

[Dave OCD]

I believe some guide books may quote this figure as it is some "rule of thumb" rcbos are prone to unwanted tripping once a 25% threshold of their rating tripping current is reached.

Are you sure, all RCBOs ? If that were the case they'd all fail the half rated current 'no trip' test and therefore be no use at all.

 

[Octopus]

I believe some guide books may quote this figure as it is some "rule of thumb" rcbos are prone to unwanted tripping once a 25% threshold of their rating tripping current is reached.

Really .............. not sure I believe that.

So how do you estimate the anticipated earth leakage of any device then?

 

[Octopus]

So if we can just slap in single up front RCD boards, what is the point of the reg in question AND why did we all start putting in dual RCD boards

Just wondering ?

Anyone?

 

[westward10]

Are you sure, all RCBOs ? If that were the case they'd all fail the half rated current 'no trip' test and therefore be no use at all.

I am only quoting a rule of thumb I believe may be quoted in a commentary/guide book which is what Paignton Pete has probably seen and stuck in his mind. 25% equates to 7.5ma for a 30ma device and it does ring a bell in my head that this should be used as a basis for circuit design. It may have some substance with the proposed 18th Ed quoting 30%.

Edit, see #57.

 

[westward10]

Thanks for that westward. I've checked your post #30. That's interesting to know.
I've now got my books out( 17th edition that is) and I still cannot find where I've think I've seen 25% of rated residual current as a design guidance. Therefore a 30mA rcd should be designed with7.5mA as its max.
I know I've seen it somewhere.

I'm wandering where the 30% 9mA came from.

Okay this is bugging me so if you have a 16th Ed copy with Section 607 in it check out Regulation 607-02-03 there you will find it.

 

[Dave OCD]

I'm sceptical about that much leakage current flowing in a healthy circuit too, unless there's a heck of a lot of I.T. equipment all going at once.

 

[westward10]

Are you sure, all RCBOs ? If that were the case they'd all fail the half rated current 'no trip' test and therefore be no use at all.

The aim here is to keep the currents at a happy level to prevent unwanted tripping, ideally an rcd/rcbo should trip under fault conditions and not excessive leakage when there is no fault. By quoting a percentage level you allow some leeway for further accumulated current and all should be good. Design a circuit where levels are excessive then any further accumulated current may result in unwanted tripping.

 

[Dave OCD]

Makes sense to me, I do think that a lot of this accumulated current can be a bit of a myth though.

 

[Deleted member 9648]

Makes sense to me, I do think that a lot of this accumulated current can be a bit of a myth though.

I work at a site where there are two IT suites each with 20-30 PC's all fed from a TPN DB with a 30ma RCD main switch. It never trips...except when it's tested.

 

[Wilko]

By the looks, the reg makes us responsible for equipment leakage in the installation design. For me to do that, the appliances would need to have a stated and rated leakage current. Or have I misunderstood?
Just now I can't recall working on a domestic dual RCD installation that was tripping for reasons other than a fault.

 

[Phil Thompson]

By the looks, the reg makes us responsible for equipment leakage in the installation design. For me to do that, the appliances would need to have a stated and rated leakage current. Or have I misunderstood?
Just now I can't recall working on a domestic dual RCD installation that was tripping for reasons other than a fault.

Same here, I'd one a fortnight ago, cheap 4way extension lead.

 

[telectrix]

I am not aware of those proposals, are you saying it is proposed that a 63a RCD would be restricted to a load of 21a?.....then presumably a 32a RCBO would be restricted to under 11a?
So a 10kw shower would need a minimum 135a RCBO ?....Sorry if I'm having a blonde moment but that just doesn't make any sense.

as i read it, it's talking about leakage currents not being more than 30% of the mA rating of the RCD, unrelated to load current.

 

[Midwest]

Since my #25 (trying not to big myself up too much here ),it has brought numerous comments and posts on 531.3.2 (draft 18th).

You'd been surprised perhaps, that the draft has only collected a few comments on this new proposed reg, which therefore may see its introduction in the 18th.

In fact the current '531.2 RCDs', will be Over Current Protective Devices. RCDs will be moved to 531.3, as far as I can make out. This includes the reg on unwanted tripping, as well as some other changes; '531.3.1.201 Except in certain special installations or locations (Part 7), for protection against electric shock, there is no requirement to disconnect/switch the neutral in TT or TN Systems'. Haven't noted that before, seem to recall members stating the opposite previously for a TT system (SP RCBO's)?

Apologies for hijacking your thread Murdoch, but you started it

 

[Octopus]

^^ ha ha.

Seeing as nobody can explain why we can fit dual board now, I have come to conclusion that my interpretation of 314.2 is correct in the op and my example stands as a non compliance to the regs.

 

[Octopus]

By the looks, the reg makes us responsible for equipment leakage in the installation design. For me to do that, the appliances would need to have a stated and rated leakage current. Or have I misunderstood?
Just now I can't recall working on a domestic dual RCD installation that was tripping for reasons other than a fault.

It's abundantly clear that the 18th will add further confusion to the regs.

Do the people who dream up these changes actually consider the impact of what they write and add. I don't think so

 

[seltechpc]

I decided to make up a small extension lead with the earth broken out so I can check the earth leakage of various plug in appliances by clamping the L+N.
It was very revealing, I checked 3 Miele appliances and found they were all around 3mA leakage; one of them was a brand new dishwasher. The leakage increased slightly when switched off on the machine. A Neff induction hob I clamped the cable and measured 2mA leakage.
These leakage currents add up and may be the reason that the proposed 18th edition is specifying a limit of 30% of the RCD trip current. Problem is I do not see how a sparky will know what appliances the householder will plug in, and will he have to check items that are hard wired like hobs. I think it is all the filters fitted to modern day electronic appliances that is giving rise to increasing leakage currents.
The only way around this, unless I am missing a trick is to fit all RCBO boards, even then you could easily exceed the 30% RCD current on 1 ring final.

 

[Midwest]

I clamped my own house the other day. PC running, few led lights on, tv on, appliance turned on but not running. Clamp meter's a cheap en, but I had 14mA leakage. But I've have that split across RCD & RCBO's. Went to a job in the afternoon, semi with 1 x lighting, 1 x RFC & electric cooker. 9mA eath leakage.

^^^ ditto

 

[Octopus]

The only way around this, unless I am missing a trick is to fit all RCBO boards, even then you could easily exceed the 30% RCD current on 1 ring final.

Hit, nail and head spring to mind..... I stopped fitting dual RCD boards when AMD3 boards arrived - far, far, far better when something trips.

 

[Deleted member 9648]

^^ ha ha.

Seeing as nobody can explain why we can fit dual board now, I have come to conclusion that my interpretation of 314.2 is correct in the op and my example stands as a non compliance to the regs.

314.2 merely states that due account shall be taken of the consequences of the operation of any single protective device

As the rest of the installation will not be affected by the operation of the device in question at the present time it complies.

 

[Midwest]

Hit, nail and head spring to mind..... I stopped fitting dual RCD boards when AMD3 boards arrived - far, far, far better when something trips.

For a larger property, I'd fit a high integrity CU with 2 or 3 RCBO's. The off the shelf RCBO populated CU's only come seem to come with 6 or so RCBO's, to make one up yourself is a tad expensive?

My own pad, which I did a few years ago, has a RCBO CU and single RCD CU for ono important circuits (314.2 considered ).

 

[Midwest]

I'd give up Murdoch

 

[Octopus]

I'd give up Murdoch

Not yet!

I need somebody to remind me why we ditched split load boards and introduced dual RCD's - somebody must have some memory of this?

Or as I said 314.2 my interpretation is correct!

There's nothing worse than a single RCD up front board ....

 

[Lucien Nunes]

Being pragmatic, I think it is most useful and sensible to have lighting and power in a given area on different RCDs and whilst one might argue about the exact interpretation of 314 it would be poor design not to do this, and hence arguably non-compliant.

The main point of a 30mA RCD is to protect against electric shock, which is most likely to occur when someone has an accident of some kind with a portable appliance. To plunge them into darkness within a fraction of a second of having been shocked, simply on the grounds of economy, is not sensible. I think we get blinkered to this purpose of RCDs because we are so used to being called on to troubleshoot nuisance trips, we don't associate their operation with the moment they cut short a possibly fatal shock that could leave someone in a vulnerable physical condition.

On the subject of convenience, many elderly and infirm people are most at risk on the stairs. They might safely be able to cross the room to turn on the ceiling light if they have been using a table lamp when the RCD serving the ring trips, but would not venture downstairs or run a cable up if the stairwell and room lighting circuits went off too.

It was very revealing, I checked 3 Miele appliances and found they were all around 3mA leakage; one of them was a brand new dishwasher.

Really? The maximum permissible on a 13A plug is 3.5mA, I would be most surprised to see that much leakage from any domestic appliance or have they gone silly with filtering these days? I don't PAT any domestics but I see a lot of PAT results from industrial equipment and no single piece of kit ever reaches 3mA. Even the media systems that I build, with maybe 20 pieces of equipment built into a rack all run from one plug, rarely reach 2mA.

 

[Octopus]

Being pragmatic, I think it is most useful and sensible to have lighting and power in a given area on different RCDs and whilst one might argue about the exact interpretation of 314 it would be poor design not to do this, and hence arguably non-compliant.

Thank you .......... which is the way I think about this subject.

Still nobody offering up why we ditched split load boards, and adopted dual RCD rather than single up front boards...............

 

[Midwest]

Really? The maximum permissible on a 13A plug is 3.5mA, I would be most surprised to see that much leakage from any domestic appliance or have they gone silly with filtering these days? I don't PAT any domestics but I see a lot of PAT results from industrial equipment and no single piece of kit ever reaches 3mA. Even the media systems that I build, with maybe 20 pieces of equipment built into a rack all run from one plug, rarely reach 2mA.

Out of curiosity, where does that figure come from?

 

[Richard Burns]

Thank you .......... which is the way I think about this subject.

Still nobody offering up why we ditched split load boards, and adopted dual RCD rather than single up front boards...............

Split load boards were relevant to the 16th Edition, protecting socket outlets with 30mA RCD protection and leaving the rest unprotected. With the advent of greater RCD protection with 17th Edition an appropriate method of protection was dual RCD boards, this addresses both the increased RCD protection required and the division of circuits guidelines in a practical way. For a domestic situation this is a practical approach, remembering the the division of circuits is worded clearly to indicate that this is not an absolute requirement.
This could be taken by common practice to be the minimum standard of compliance with the regulations.
It is always possible to exceed the minimum standard and fit an all RCBO board. I think there would be no doubt that this provides a greater division of circuits but at present the cost benefit analysis is still wavering and comes down in favour of the dual RCD board (by my analysis, but not by yours). As the cost of RCBOs comes down this will, and is, shifting the balance of what is reasonably practicable.

I would say that overall in a domestic property a single dual RCD board or two upfront RCD boards is compliant but a single all RCBO board would exceed the minimum requirements.

 

[Octopus]

S
It is always possible to exceed the minimum standard and fit an all RCBO board. I think there would be no doubt that this provides a greater division of circuits but at present the cost benefit analysis is still wavering and comes down in favour of the dual RCD board (by my analysis, but not by yours).

If I'm challenged about my preference for fitting RCBO boards - I explain what happens when 1 RCD trips on a dual board - and most people then agree RCBO boards are better.

As for minimising inconvenience and 314.2 all it would take is 1 or 2 more sentences in 7671 to clarify.

I will continue not to fit small up front boards if the circuits contained in the the same room(s).

Last month I was working on an older MK split load board - instead of moving a circuit from the non RCD side to the RCD side, I opted to fit a RCBO - sure it cost the client about £50 but much better in the long run.

Personally I'd like to see boards split RCD / RCBO .......... sockets on RCBO's

 

[Lucien Nunes]

Out of curiosity, where does that figure come from?

543.7.1.1

 

[Deleted member 9648]

I think the view that the installation in the original post is non compliant is being rather overlapped with the view that there is a better design alternative.
The two are entirely different things. Yes there is a better design alternative, but given that there is a division of circuits over the installation as a whole, it is compliant.
Like a lot of Bs7671 314.2 is open to various interpretations and does not specifically state that circuits within the same room must not be subject to loss from a single protective device.

 

[Risteard]

I need somebody to remind me why we ditched split load boards and introduced dual RCD's - somebody must have some memory of this?

Because under the 16th Edition we didn't tend to RCD protect everything.

 

[Ian1981]

SPlit load dual rcd consumer units came out when the 17th edition introduced the requirement for more rcd protected circuits for multiple reasons as with the 16th cables where not required to have additional protection to them where buried in walls <50 mm

 

[seltechpc]

Really? The maximum permissible on a 13A plug is 3.5mA, I would be most surprised to see that much leakage from any domestic appliance or have they gone silly with filtering these days? I don't PAT any domestics but I see a lot of PAT results from industrial equipment and no single piece of kit ever reaches 3mA. Even the media systems that I build, with maybe 20 pieces of equipment built into a rack all run from one plug, rarely reach 2mA.

I decided to recheck these readings and the results were 1.2mA, 1.3mA and the newest appliance was 1.96mA. A bit red faced at quoting 3mA but these do add up to almost 4.5mA. The hob was around 2mA which starts to seem these electronic appliances with various filters to meet EMC specs are increasing the leakage currents to levels where it can lead to unwanted tripping of the RCD's, even with a high integrity CU.
Add more appliances and a few computers and little thought given to which rings they are plugged into can give rise to nuisance tripping.

 

[Octopus]

SPlit load dual rcd consumer units came out when the 17th edition introduced the requirement for more rcd protected circuits for multiple reasons as with the 16th cables where not required to have additional protection to them where buried in walls <50 mm

I realise this but why a dual RCD and not a single up front RCD?

 

[Midwest]

I realise this but why a dual RCD and not a single up front RCD?

I don't think this kind of subterfuge, is going to work Murdoch

 

[Ian1981]

Then you run the risk of losing all your power if the rcd trips.
At least with 2 you don't loose all power to all circuits.
Of course you can do that arrangement if you wish but I know you wouldn't
I haven't read the full thread so I feel I'm missing the point?

 

[Ian1981]

Or do you feel only rcbos are the only solution?
Each individual circuit?

 

[Octopus]

Then you run the risk of losing all your power if the rcd trips.
At least with 2 you don't loose all power to all circuits.
Of course you can do that arrangement if you wish but I know you wouldn't
I haven't read the full thread so I feel I'm missing the point?

Have you read my opening post ?

 

[Ian1981]

Db for the loft sockets and lights on one rcd.
Your worried about loss of power to the whole loft.
I'd say that it's fine.
The rest of the house wouldn't be affected I wouldn't be worried about it.
I see the point in individual rcbo protection but individual rcd protection for all circuits isn't a requirement tho certainly not prohibited.
Upto the individual installer I'd say.

 

[Deleted member 26818]

I think the reason we went from split boards to dual RCD boards is simply down to manufacturers.
Cheaper to alter existing stock to dual RCD than to bin it all and start manufacturing high integrity boards.

 

[Octopus]

Db for the loft sockets and lights on one rcd.
Your worried about loss of power to the whole loft.
I'd say that it's fine.
The rest of the house wouldn't be affected I wouldn't be worried about it.
I see the point in individual rcbo protection but individual rcd protection for all circuits isn't a requirement tho certainly not prohibited.
Upto the individual installer I'd say.

So why don't we fit single up front rcd boards any more then?

 

[Deleted member 26818]

So why don't we fit single up front rcd boards any more then?

Did we ever?

 

[Ian1981]

So why don't we fit single up front rcd boards any more then?

Think I've already answered that one murdoch.
Risk of TOTAL loss of power as opposed to partial loss with a dual board.

 

[Ian1981]

Did we ever?

I never

 

[Octopus]

Risk of TOTAL loss of power as opposed to partial loss with a dual board.

Which neatly brings us back to my opening post ...... I rest my case.

 

[Ian1981]

Which neatly brings us back to my opening post ...... I rest my case.

but the rest of the house still functions yes?

 

[Midwest]

Still go back to the original design for this install. Single RCD for both lighting & power for a loft conversion. Would 'you' put those circuits on the same RCD in the CU, if there was space?

 

[Deleted member 26818]

The thing is Murdoch, 314 requires us to minimise inconvenience, it doesn't require us to eliminate it.

 

[Ian1981]

Why does the loft need to be on its own circuit as in lights in particular?